Measurement and definitional issues loom large when discussing patient
safety. The bellwether 1999 Institute of Medicine report To Err Is Human provided compelling evidence that medical errors pose
daily risks throughout the US health care system but failed to quash controversy
about the magnitude of that risk.1 The best-known
estimates of the extent of medical error rely on extrapolations from medical
record review studies,2,3 although
these numbers have generated heated debate.4- 6